A series of four epidemiologic studies are intended to evaluate the possible effects on human reproduction of low-dose radiation exposure. The individual studies are designed to specifically examine the relationship of radiation exposure to birth defects, spontaneous abortion, fetal and infant death, childhood cancer and human growth and development. Each of the studies focuses on different possible reproductive outcomes, but the studies and the study populations overlap and will provide complementary data. Two general populations are being studied. These are a cohort of nuclear workers (female workers and wives of male workers) who are occupationally exposed to low levels of radiation (external and internal exposures), and a cohort of births to nuclear workers. Data for all segments of the study will be collected using medical records, vital records, subject interviews, employment records or a combination of these sources.